21,139 reputation
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bio website lightandmatter.com
location Fullerton, California
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I teach physics at Fullerton College, a community college in Southern California. I have an undergrad degree in math and physics from Berkeley and a PhD in physics from Yale. Back when I was doing research, my field was experimental low-energy nuclear physics.


Aug
14
answered A common definition of a scalar
Aug
14
comment Are there two theories that are mathematically identical but ontologically different?
Aren't there solid-state-physics analogs of black holes?
Aug
14
comment Are there two theories that are mathematically identical but ontologically different?
String theory is not mathematically identical to the standard model.
Aug
14
comment How is it that a tachyon is faster than $c$?
related: physics.stackexchange.com/q/61126
Aug
14
comment How is it that a tachyon is faster than $c$?
Such a particle would indicate that we fundamentally misunderstand the structure of spacetime, since travel faster than c is forbidden in special and general relativity. Not true. There are specific issues with FTL in SR, but this is not a correct statement of any of them.
Aug
13
comment What's the biggest cube you could have before gravity rounded it?
@Kyle: I don't think that's necessarily true. The Swiss cheese version would have a lower density, but it would also have a lower shear strength, wouldn't it? The result depends on $\rho^{-1}Y^{1/2}$. It would be interesting to understand how that product scaled with Swiss-cheesing.
Aug
13
revised Why does the Sun's (or other stars') nuclear reaction not use up all its “fuel” immediately?
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Aug
13
comment Why does the Sun's (or other stars') nuclear reaction not use up all its “fuel” immediately?
Good point, +1. I would say that this is orthogonal to the other answers, which start from assumed conditions of pressure and temperature at the sun's core. However, the fact that the sun is in a stable equilibrium isn't the only difference between the sun and an H-bomb. The other differences include the need for the weak interaction and quantum-mechanical tunnelling.
Aug
13
comment Why does the Sun's (or other stars') nuclear reaction not use up all its “fuel” immediately?
@Tyzoid: How does one go about doing that?
Aug
13
comment What's the biggest cube you could have before gravity rounded it?
related: skeptics.stackexchange.com/questions/5848/…
Aug
13
revised What's the biggest cube you could have before gravity rounded it?
added 584 characters in body
Aug
13
revised What's the biggest cube you could have before gravity rounded it?
added 2 characters in body
Aug
13
comment What's the biggest cube you could have before gravity rounded it?
After my first comment, it looks like MariusMatutiae changed $l_{crit}$ from 10 km to 1000 km and inserted a G in the equation. After those changes, the answer looks similar to my own answer, so I think we're in agreement.
Aug
13
answered What's the biggest cube you could have before gravity rounded it?
Aug
13
comment What's the biggest cube you could have before gravity rounded it?
I don't think this calculation is right. The final expression doesn't have $G$ in it, and therefore it doesn't have any input that depends on how strong gravity actually is in our universe. This seems to have happened because of the reasoning involving $q'$, which doesn't make sense to me. "the acceleration this matter feels is a fraction q′≈0.1 of the local acceleration of gravity" I don't understand why it would feel less than the full, local value of g...?
Aug
13
comment What's the biggest cube you could have before gravity rounded it?
This seems considerably too small. For instance, Vesta has a diameter of 500 km, but it has a highly irregular potato shape.
Aug
13
comment What's the biggest cube you could have before gravity rounded it?
Although this does give a number in the right ballpark, I don't think the logic is correct. The gravitational binding energy you're using is the difference between the surface and infinity, which isn't relevant to the object's internal structure. What I think you've actually estimated here is the size of an object whose gravity well is deep enough so that if further material accretes onto it by gravitational collapse (starting from rest, far away), the material will be vaporized on impact.
Aug
13
comment Is it possible to derive Lorentz transformation equation without Einstein's postulates?
possible duplicate of What axiomatizations exist for special relativity?
Aug
13
revised What are the similarities and differences between speech and music sounds?
added 211 characters in body
Aug
13
answered What are the similarities and differences between speech and music sounds?